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5532 1st order bandpass for electret mic preamp

I found the capacitors that give the desired response.  The mic runs straight into the non-inverting, with R1 at 50k and R2 at 10k in the negative feeback loop.  It works perfectly but when I attempt to increase the gain by increasing the value of R1 but does not gain as it should, even at 100k.

I had tried the awesome SSM2219 and had no problems with the one-resistor gain adjustment.  I was able to pick up dogs barking two block away with just the window in the room open. So does the resistor combination have to change for extended gain ranges or are the caps influencing the feedback?

The band is about 500-3500Hz, first order.  The application is a speech recognizer which requires the substance of 300Hz-10khz.  However, the electret's frequency response is not flat, and begins to rise substantially after 3500Hz.  The lows are being attenuated to reduce background noise, and also the highs to some extent, but this particular electret takes a dive after 10kHz anyway.

Any pointers will be appreciated.

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  • If you are interested in using our MEMS microphones for your design, I would recommend either the ADMP404, which has a flat frequency response from 100 Hz to 15 kHz, or the ADMP504, which has a very high SNR of 65 dB. It looks like you're using a large array of microphones, so MEMS mics may be attractive for your design because their frequency responses are typically very well-matched from part-to-part and their sensitivity over time and temperature is much more stable than that of ECMs. The details of these and some other advantages of MEMS microphone technology over ECMs is detailed in our application note AN-1003.

    We don't have any documentation to specifically describe connecting analog MEMS microphones to the SSM2019, but the following app note and Circuit from the Lab may be useful:

    AN-1165: Op Amps for MEMS Microphone Preamp Circuits

    CN-0262: Low Noise Analog MEMS Microphone and Preamp with Compression and Noise Gating (describes the connection between an ADMP504 microphone and SSM2167 preamp)

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  • If you are interested in using our MEMS microphones for your design, I would recommend either the ADMP404, which has a flat frequency response from 100 Hz to 15 kHz, or the ADMP504, which has a very high SNR of 65 dB. It looks like you're using a large array of microphones, so MEMS mics may be attractive for your design because their frequency responses are typically very well-matched from part-to-part and their sensitivity over time and temperature is much more stable than that of ECMs. The details of these and some other advantages of MEMS microphone technology over ECMs is detailed in our application note AN-1003.

    We don't have any documentation to specifically describe connecting analog MEMS microphones to the SSM2019, but the following app note and Circuit from the Lab may be useful:

    AN-1165: Op Amps for MEMS Microphone Preamp Circuits

    CN-0262: Low Noise Analog MEMS Microphone and Preamp with Compression and Noise Gating (describes the connection between an ADMP504 microphone and SSM2167 preamp)

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